Nitride semiconductors such as GaN, AlN, InN, a mixed crystal thereof have characteristics such as a high saturation electron velocity and a wide band gap. Accordingly, various studies have been made on application of the nitride semiconductors to high-output and high-efficiency amplifiers and high-frequency devices and so on by utilizing these characteristics.
As a semiconductor device using the nitride semiconductor, there are a lot of reports as for a field-effect transistor, particularly as for a high electron mobility transistor (HEMT). For example, operations at a shallow threshold voltage are demanded for the HEMT. It is effective to make an insulating film between a gate electrode and a channel thin to enable the operations at the shallow threshold voltage. However, a gate leakage current may be large, or a withstand voltage may be lowered if the insulating film is made thin. A semiconductor device is proposed where fluorine-ion is contained in a whole of the insulating film to enable normally-off operations, but a sheet resistance is extremely high in this semiconductor device.
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